1. Field of the Invention:
The present invention relates to a fixed speed cruising control apparatus for a vehicle to automatically keep cruising speed of the vehicle constant.
2. Discussion of Background:
FIG. 7 is a diagram showing a conventional fixed speed cruising control apparatus disclosed, for instance, in Japanese Unexamined Patent Publication No. 39311/1983. In FIG. 7, a reference numeral 1 designates a set switch operable by a driver to command initiation of a fixed speed cruising, a numeral 2 designates a cancel switch which is actuated by operating a braking device (not shown), whereby instructions of cruising at a fixed speed is cancelled, and a numeral 3 designates a vehicle speed sensor to detect cruising speed of a vehicle (not shown). The sensor 3 comprises a rotating body 3a having four magnetic poles and a lead switch 3b. The rotating body 3a is rotated by a meter cable (not shown) for transmitting revolution of a transmission (not shown), and outputs a signal consisting of a pulse train having a frequency in proportion to the cruising speed. A numeral designates a car battery, a numeral 5 designates a main switch as a power source switch to feed electric power in the car battery 4, a numeral 6 designates a control apparatus which is actuated by the operation of the main switch 5 and which includes a processing circuit 6a constituted by, for instance, a micro-computer. The control apparatus 6 receives signals from the set switch 1, the cancel switch 2 and the speed sensor 3 and performs processing of the signals so that the cruising speed vs of the vehicle is brought to the target speed vr, whereby various control signals are outputted to carry out automatic control for the speed of the vehicle. A numeral 7 designates a motor-driven type throttle actuator which receives various control signals from the control apparatus 6 and which opens and closes through a link 7a and a motor (not shown) a throttle valve 9 which is disposed in an air intake passage 8 for an engine (not shown), and is operable in association with an accelerator pedal (not shown). The link 7a is connected to the motor by means of an electromagnetic clutch (not shown). Connection and disconnection of the link 7a to the motor is controlled by a signal from the control apparatus 6.
The operation of the conventional fixed speed cruising control apparatus having the construction as above-mentioned will be described.
On actuation of the main switch 1 by the driver, electric power in the car battery 4 is supplied to the control apparatus 6. Then, the control apparatus 6 processes output a signal of the speed sensor 3. The speed sensor 3 outputs a signal of pulse train having a frequency in proportion to the cruising speed vs of the vehicle. By measuring the frequency of the signal in the control apparatus 6, the actual cruising speed vs is calculated.
When the driver operates the main (set) switch 1, the signal of the switch 1 is supplied to the control apparatus 6 in which the cruising speed vs at that time is memorized as a target speed vr and then, control for the fixed cruising speed is started. The control apparatus 6 compares the actual cruising speed vs supplied at every moment with the target speed vr and outputs a control signal to have the vehicle travel at the target speed vr. The throttle actuator 7 is actuated by the control signal to adjust the degree of opening of the throttle valve 9. Namely, when the actual speed vs is lower than the target speed vr, a signal for opening the throttle valve is generated to open the valve 9 by a predetermined aperture. On the other hand, when it is higher than the target speed, a signal for closing the throttle valve is generated to close the valve 9 by a predetermined aperture. Accordingly, the vehicle travels at a fixed speed without operating the accelerator pedal.
When the driver operates the braking device during the controlling operation for the fixed speed cruising, the cancel switch 2 is actuated by which a signal for reducing the fixed speed cruising is supplied to the control apparatus 6. Then, the control apparatus outputs a signal for braking the electromagnetic clutch, and the clutch is disengaged by the throttle actuator 7 as soon as it receives the signal. Thereafter, the driver adjusts the degree of opening of the throttle valve by the accelerator pedal to thereby control the cruising speed.
In the conventional fixed speed cruising control apparatus having the construction as above-mentioned, the cruising speed signal from the speed sensor 3 changes by various causes even when the vehicle travels at a certain fixed speed. In this case, a control signal is outputted to correct deviation caused between the actual cruising speed vs and the target speed vr, whereby the throttle actuator 7 is actuated. When the throttle valve is controlled to be opened or closed by the actuator 7, the driver and passengers feel uncomfortableness due to acceleration and decceleration of the vehicle.
It is considered that unstable outputs of the speed sensor 3 are resulted from, for instance, eccentricity of the revolution center of the rotating body 3a of the speed sensor 3, or uneven rotation of a wire cable for connecting the transmission to the rotating body 3a, in addition to electric noises which are generated inside or outside the vehicle. The unstable outputs of the speed sensor 3 depend on the revolution number of the rotating body 3a, i.e. cruising speed. Further, characterstics of the sensor largely affects the unstable outputs. To eliminate such disadvantage, there has been known a method of smoothening the cruising speed signal by a low-pass filter to thereby reduce the electric noises. However, use of the low-pass filter greatly reduces response of a control system because it is necessary to use the low-pass filter having a large time constant. Thus, in the conventional apparatus, it was very difficult to satisfy both conditions of reducing the electric noise components and maintaining high response properties of the control system.